1. Technical Field
The present invention relates to a technique for copying a content recorded on a first recording medium, onto a second recording medium, and in particular to a technique for selecting and copying a part of the content.
2. Background Art
Commercial contents such as movies and music are attached with digital signatures to prove the validity of the contents. Playback devices verify the digital signatures when playing the contents, and perform a process for playing the contents after the legitimacy of the contents is proved.
In a case where the content is recorded onto a Blu-ray Disc (which is a registered trademark, and is abbreviated as BD hereinafter BD-ROM), a digital signature is generated based on the digest values of all the data pieces (hereinafter referred to as “clip”) that are obtained by dividing the content into data pieces each having a certain size, and calculating the digest values of the respective data pieces. The generated digital signature obtained in the above-described manner is recorded on the BD-ROM with the content, and provided to a user. Here, the BD-ROM has recorded thereon a digest value table, in addition to the content and the digital signature. The digest value table stores the digest values of the respective clips that constitute the content.
Then, when playing the content, the playback device performs a signature verification process in the following manner.
The Playback Device
(1) arbitrarily selects a predetermined number of clips from among the clips constituting the content, and calculates the digest values of the selected clips,
(2) acquire, from the digest value table, digest values of clips that are not selected, and
(3) performs signature verification with use of (i) the digest values calculated from the selected clips, (ii) the digest values acquired from the digest value table, (iii) the digital signature recorded on the BD-ROM, and (iv) a key used for the signature verification that has been stored in the playback device in advance.
Since the playback device arbitrarily selects clips in the process (1) described above, the digest value table is required to store the digest values of all the clips, so as to accommodate whichever digest value is selected.
Also, users cannot copy the commercial contents, since the commercial contents are protected from unauthorized copying, with use of encryption techniques.
However, there has been considered a service for permitting the legal copying of the commercial contents on the condition that a billing process or the like is performed.
In the case of considering the service for permitting legal copying of the commercial contents, when the content on the BD-ROM is recorded onto a recording medium (which is sometimes referred to as “BD-R/RE” hereinafter) such as BD-R (BD-Recordable), and BD-RE (BD-Rewritable), it is preferable that clips can be recorded such that only clips including user's favorite scenes are selected and recorded, in addition to a case where the whole content recorded on the BD-ROM is copied.    Patent Document 1: Japanese Patent Application Publication No. 2001-75930;    Patent Document 2: Japanese Patent Application Publication No. 2004-72792; and    Non-Patent Document 1: Advanced Access Content System (AACS) Pre-recorded Video Book Revision 0.91 Feb. 17, 2006.